This invention is generally directed to electroreceptors, and more specifically the present invention is directed to electroreceptors comprised of amorphous hydrogenated silicon carbide alloys (a-SiC:H) containing between about 10 and 60 atomic percent carbon, between about 10 and 60 atomic percent hydrogen, and between about 10 and 80 atomic percent silicon and processes for the preparation thereof. The aforementioned electroreceptors possess, for example, minimal dark conductivity of less than or equal to 10.sup.-12 .OMEGA..sup.-1 -cm.sup.-1, and specifically from about 10.sup.-12 .OMEGA..sup.-1 -cm.sup.-1 to about 10.sup.-20 .OMEGA..sup.-1 -cm.sup.-1, and negligible photoconductivity of less than or equal to 10.sup.-9 .OMEGA..sup.-1 -cm.sup.-1 at 10 ergs/cm.sup.2, and specifically from about 10.sup.-9 .OMEGA..sup.-1 -cm.sup.-1 to about 10.sup.-20 .OMEGA..sup.-1 -cm.sup.-1. In one specific embodiment of the present invention there is provided an amorphous hydrogenated silicon carbide electroreceptor with about 25 atomic percent of carbon, about 35 atomic percent of silicon, and about 40 atomic percent of hydrogen. Other characteristics associated with the mechanically resistant electroreceptors of the present invention include an optical bandgap exceeding or equal to 2 electron volts, and specifically from between about 2.0 and about 3.5 electron volts, and the ability to sustain electrical fields of up to 100 volts per micron with no observable breakdown or loss of electrical potential under ambient light with films that are, for example, between about 10 and 120 microns in thickness. The aforementioned electroreceptors of the present invention are useful in ionographic imaging and printing systems such as those commercially available as the Xerox Corporation 4060.TM. and 4075.TM. , which utilize an electrically resistive dielectric image receiver, that is an electroreceptor. In one simple form of these systems, latent images are formed by depositing ions in a prescribed pattern onto the electroreceptor surface with a linear array of ion emitting devices or "ion head" creating a latent electrostatic image. Charged toner particles are then passed over these latent images causing the toner particles to remain where charge has previously been deposited, and sequentially this developed image is transferred to a substrate such as paper, and permanently affixed thereto with, for example, radiant, hot roll, pressure fusing or combinations thereof.
Numerous different members have been proposed for imaging processes including, for example, hydrogenated amorphous silicon containing carbon therein, reference for example U.S. Pat. Nos. 4,461,820 and 4,226,898, which discloses an amorphous semiconductor film with desirable photoconductive properties comprised of silicon tetrafluoride, see column 7, line 9. Also, in column 19, line 66, to column 20, line 7, there is disclosed the selection of SiH.sub.6 and C.sub.2 H.sub.6 in an atmosphere of F.sub.2 to provide a host matrix of a silicon-carbon alloy, which is altered by the inclusion of hydrogen and fluorine. In the '820 patent, there is described an electrophotographic image forming member with a photoconductive layer of an amorphous material containing at least one of hydrogen atom and halogen atom in a matrix of silicon atom, and wherein the photoconductive layer contains at least one of oxygen atom, nitrogen atom, and carbon atom, see the Abstract of this patent for example. The carbon atoms are present in an amount from about 0.001 to about 20 atomic percent, reference column 3, lines 20 to 23, of the '820 patent. Also of interest are U.S. Pat. Nos. 4,532,199; 4,668,599; 4,378,417; 4,377,628; and 4,696,884 (see for example column 11, lines 30 to 36, wherein it is indicated that the amount of (OCN) contained in the layer region is preferably from about 0.001 to 50 atomic percent). Each of these references, however, relate to electrophotography with a photoconductive imaging member, and do not appear to describe the use of these materials as an electroreceptor that can be selected for ionographic processes, the main aspect of the present invention.
The aforementioned ionographic member device, or electroreceptor of the present invention possesses substantially different properties than that exhibited by, for example, a-SiC:H materials that are selected as a photoreceptor for use in electrophotography. Specifically, electrophotographic imaging processes utilize light to form the latent image on the imaging member, thus a photoconducting member is selected. Also, electrophotography usually requires photoreceptors with high photosensitivity and panchromaticity. Further, in most applications there is substantial dark decay associated with the photoreceptor member because of its semiconducting characteristics. In addition, the ability to transport charge carriers of at least one polarity is needed with photoreceptors. Regarding the a-SiC:H materials utilized as blocking layers, it is generally advantageous for such layers to be able to transport one sign of charge carriers, or to be extremely thin (from about 100 to about 5,000 Angstroms) to permit discharge potential by such processes as tunneling. In this manner, residual charge is not built up at layer interfaces thereby causing poor imaging.
Ionographic imaging in its simplest form, in contrast, creates the latent image by "writing" with an ion head on the surface of the imaging member, which member is to be electrically insulating so that the charge applied by the ion head does not disappear prior to development. Therefore, ionographic receivers possess negligible, if any, photosensitivity. The absence of photosensitivity provides considerable advantages in ionograhic applications. For example, the electroreceptor enclosure does not have to be completely impermeable to light and radiant fusing can be used without having to shield the receptor from stray radiation. Also, the level of dark decay in these ionographic receivers is characteristically low (from 0 to 3V/sec (volts/second) at electrical fields of 10 to 50V/.mu.m) thus providing a constant voltage profile on the receiver surface over extended time periods. Further, with electroreceptors overall, charge transport of either positive or negative carriers is somewhat limited, with carrier transport ranges being less than about 10.sup.-10 cm.sup.2 /V.
There are thus important differences in the physical characteristics of the a-SiC:H electroreceptors of the present invention, and known photoreceptors selected for electrophotographic imaging purposes. The a-SiC:H materials utilized in photoreceptors for electrophotography possess, for example, excellent photosensitivity when applied as photogeneration layers and transport only one sign of charge carriers when applied as blocking layers. In contrast, the a-SiC:H electroreceptors of the present invention possess no significant photosensitivity or ability to transport charge, enabling, for example, high charge acceptance (.gtoreq.20V/.mu.m, and specifically from about 50 to 100V/.mu.m) and a constant voltage profile with time independent of the ambient environment.
Dielectric receivers selected for imaging and printing systems, such as the commerically available Xerox 4060.TM. and 4075.TM. are characterized by high electrical resistivity, low photosensitivity, and resistance to abrasion and environmental effects. The material selected for these printing systems is comprised of aluminum oxide, which is usually applied as a 30 .mu.m (microns) thick film on a cylindrical receiver. These layers, although adequate for their application, are considered undesirable because of their inherent inhomogeneity. The numerous physical cracks in the material, which unavoidably occur in the thin film deposition process, must be filled with a softer material which does not possess the desirable characteristics of the optimum electroreceptor material, such as extreme hardness and chemical inertness. Furthermore, the oxide materials exhibit an undesirable sensitivity to humidity in the ambient environment causing an uncontrolled loss of, and spreading over the surface of the charge contained in the latent image on the receptor. These characteristics necessitate the use of heater elements incorporated in the electroreceptor device.
Therefore, there remains a need for electroreceptors with improved characteristics. Additionally, and more specifically there remains a need for simple, economical plasma deposited hydrogenated amorphous silicon carbide (a-SiC:H) electroreceptors with between about 10 and 60 atomic percent carbon, between about 10 and 60 atomic percent hydrogen, and between about 10 and 80 atomic percent silicon with minimal dark conductivity of .ltoreq.10.sup.-12 .OMEGA..sup.-1 -cm.sup.-1, and specifically, for example, from about 10.sup.-12 .OMEGA..sup.-1 -cm.sup.-1 to about 10.sup.-20 .OMEGA..sup.-1 -cm.sup.-1, and negligible photoconductivity of .ltoreq.10.sup.-9 .OMEGA..sup.-1 -cm.sup.-1 at 10 ergs/cm.sup.2, and specifically, for example, from about 10.sup.-9 .OMEGA..sup.-1 -cm.sup.-1 to about 10.sup.-20 .OMEGA..sup.-1 -cm.sup.-1, and processes for the preparation thereof. Moreover, there remains a need for hydrogenated amorphous silicon carbide electroreceptors with high charge acceptance of .ltoreq.20 V/.mu.m, and specifically, for example, from about 50 to 100 V/.mu.m, and low dark decay of .gtoreq.5 V/sec, and specifically, for example, from about 0 to 5 V/sec at electric fields of about .gtoreq.20 V/.mu.m. There also is a need for a-SiC:H electroreceptors with excellent mechanical properties, particularly hardness and resistance to mechanical wear, enabling the electroreceptor to be selected for extended time periods, exceeding 1,000,000 imaging cycles. In addition, there is a need for a-SiC:H electroreceptors with a low dielectric constant of .ltoreq.7, and specifically, for example, from about 2 to 7, which assists in charging the surface of the receiver. Also, there remains a need for electroreceptors which are not sensitive to humidity, for example, from about 20 to about 80 percent relative humidity, and temperature of the ambient environment.